This invention concerns twin sheet thermoforming machines and more particularly platen drives for platens included in a forming station. In the forming station, upper and lower molds are carried by upper and lower platens respectively for forming separate part halves in a well known manner. After the part halves are formed, the upper and lower platens are moved together to fuse the two part halves together. This process and such thermoforming machines are described in U.S. Pat. Nos. 5,814,185 and 6,969,246 assigned to the same assignee as the present application, and are incorporated herein by reference.
It is critical that the molds mate perfectly in order to produce a uniform seam thickness for such a twin sheet molding process when the platens are advanced together, and this requirement in turn requires both platens to be perfectly level to be parallel when fully advanced, partially with large platens.
However, it is difficult to achieve level platens with large area platens and requires extremely time consuming manual adjustments requiring disassembling of gearing. The meshing of drive gearing with fixed gear rack guide posts typically used to guide the platen motion makes this very slow, difficult and time tedious since variations of the degree of engagement of the drive unit gearing engagement with the four gear racks affects the level condition of such a platen, i.e. a greater degree of engagement slightly elevates the associated platen and a lesser degree of engagement slightly lowers the platen changing the degree of gear engagement with one post may affect another gear-post engagement.
In addition, the perfectly plumbed guide gear rack posts engage guide bushings on the platens during travel of the platens, and even a slight out of level condition would create significant binding in the post/sleeve engagement surfaces, particularly in large area platens and result in rapid wear of the guide bushings to significantly increase maintenance costs.
Conventional platen drives involve one or two motors driving respective sets of gearing which engage associated fixed gear posts to drive the platens.
Machining a large platen is costly as very large machining centers are required to accommodate such platens and align bores at either end of the platen for the respective gearing.
Accordingly, it is an object of the present invention to provide a method for the leveling platens in a thermoforming machine station which reduces the time and difficulty of setting the platens level.
It is a further object to provide a platen drive for thermoforming machine forming station platen which allows simplified leveling of the platens and also lower a cost manufacture of the platens.